The present invention relates to a sailboat and more particularly to a sailboat having a rotatable mast which spreads out a main sail and the other sails so that the mast itself can share a part of a wing-shaped leading edge for producing a dynamic lift.
Sailing vessels have a long history. Once the most commonly used was a four-sided sail spreading between a boom and a spar sticking abaft the upper point of the mast, until recent technical developments of sailing have brought about the Marconi rig with a tall triangle-shaped sail. Nowadays the most popular sails are equipped in such a way that the luff, i.e. the front side of the mainsail is led to a groove formed along the back side of the mast, while the foot of the mainsail is led to a groove formed along the upper edge of the boom.
In other words, in a sailing vessel thus equipped, for example a yacht, the sail not only becomes easier to handle but also enables more efficient sailing by spreading the sail between the mast and the boom in an ideal shape. This is the reason for its popularity among racers.
FIG. 1 shows an example of a mast used on existing yachts equipped as described above. A mast 1 is in the form of a pipe and has a hollow space 2 in consideration of the need of light weight and strength. Generally the mast 1 has an integrated unit with taper made of laminated wood, light metals and plastic materials. Reference numeral 3 denotes a groove provided along the back side of the mast 1. The groove 3 is narrow-mouthed to prevent the front part 5A of a sail 5, with the luff rope 4 contained inside of the groove 3, from flying out.
Thus, when setting the sail, a downward pull at the main halyard installed through a pulley at the top of sail 5 lifts the front side 5A of the sail 5 to the top of the mast 1 along the groove 3.
However, in the prior mast 1 thus constructed, the mast 1 is fixedly mounted to the hull of the sailboat and accordingly the direction of the mast 1 is not variable. As a result, the lift in the sail 5 that bears a driving force works only in a portion of the sail 5 that spreads backward from the groove 3, and the mast 1 itself does not contribute to the lift.
Moreover, depending on the directions of a wind and the sail 5, complex vortex and/or exfoliation of a laminar layer can be formed behind the mast 1 and the sail 5, reducing lift, sometimes resulting in a stall.
Furthermore, in case of reefing or folding the sail, although some sails are designed to be rolled around the boom, usually this is a hard work without a proper equipment.